The invention relates to visual display systems and in particular to flat-panel displays produced using micro-machining techniques
Flat-panel video displays are ubiquitous components of many consumer, industrial and military products and devices. They are found in computer laptops, automobile dashboards, microwave ovens and a myriad of other machines and devices with which man interacts.
Active-matrix liquid-crystal displays dominate the market for high quality high-resolution flat-panel displays. However, these displays are relatively expensive and the amount of power they consume when operating is relatively large in comparison to the amount of power readily available from many battery driven devices.
The need and desire to incorporate visual displays into more and more products, ranging from portable GPS baedekers to toys, has created a strong demand and expanding market for inexpensive flat-panel displays that can provide high quality images and operate with low power consumption.
In response to the demand, new types of flat panel displays have been developed based on the processing of silicon using MEMS technology. MEMS technology enables microstructures having features on the order of a few microns to be formed on appropriate silicon substrates. The technology can therefore be used to produce xe2x80x9cpixelxe2x80x9d sized devices, on silicon, that process light. Arrays of these devices are useable to form flat-panel displays that are potentially inexpensive, that operate with low energy consumption and provide high-quality images.
Most flat-panel displays produced using silicon technology belong to one of two general types. A flat-panel display of a first type has pixels each of which comprises a liquid crystal cell formed on a silicon substrate. Light, which may be ambient light or light from an appropriate light source, illuminates the pixels. Transmittance of the liquid crystal in each pixel for the light determines how bright the pixel appears. The transmittance of the liquid crystal is controlled by voltage on electrodes in the pixel. A pattern of pixels having varying levels of brightness is formed on the display to produce an image by controlling the voltage on the electrodes in each pixel of the display. Images provided by this type of display generally suffer from low brightness and low contrast.
A flat panel display, hereinafter referred to as a xe2x80x9cmicro-mechanical displayxe2x80x9d, of a second type, has pixels each of which comprises at least one movable structure micro-machined on a silicon substrate. The position of the at least one moveable structure in each pixel controls how bright the pixel appears by controlling an amount of light that the pixel reflects or diffracts. Generally, the position of the at least one moveable element is controlled by electrostatic forces between the at least one moveable element and electrodes in the pixel that are generated by applying appropriate voltages to the electrodes. Often the voltages are relatively high and moving the at least one moveable element requires a relatively large expenditure of energy. Usually, in these types of displays, brightness and image contrast are dependent upon viewing angle, as measured with respect to the normal to the plane of the display, and decrease as the viewing angle increases. Some of these displays require an internal light source that consumes relatively large amounts of power when operating.
A micro-mechanical display in which the at least one moveable structure in pixels in the display comprises a plurality of parallel flexible reflecting ribbons is described in U.S. Pat. No. 5,841,579 to D. M. Bloom et al, which is incorporated herein by reference. The flexible ribbons in a pixel of the display are normally located parallel to the plane of the substrate on which the pixel is formed at a small distance above the plane. The ribbons are controllable to be depressed towards the substrate by electrostatic forces that are generated by voltages applied to electrodes in the pixel.
To form an image on the display, the pixels in the display are illuminated with light from a suitable light source so that light is incident on the pixels at a given angle with respect to the plane of the display. When alternate ribbons of the plurality of ribbons in a pixel are depressed, the plurality of ribbons in the pixel form a diffraction grating that diffracts some of the incident light at an angle such that the pixel appears bright to a user of the display. If alternate ribbons are not depressed, the plurality of ribbons in the pixel reflect the incident light at a different angle such that light from the pixel does not reach the eye of the user and the pixel appears dark. An appropriate pattern of bright and dark pixels forms the image on the display. The patent describes methods for using pixels of the type described to produce a flat-panel displays that provide color images.
Another type of micro-mechanical display is described in U.S. Pat. No. 5,636,052 to S. C. Arney et al, which is incorporated herein by reference. In this flat-panel display the at least one moveable element in a pixel is a membrane. The membrane is flexibly supported so that it is parallel to the substrate with a small air gap between the two. Light that is incident on the pixel is reflected by both the substrate and the membrane. The height of the air gap determines whether the reflected light from the membrane and the substrate interfere constructively or destructively and therefore if the pixel appears bright or dark respectively. An addressable electrode in the pixel, when charged attracts the membrane towards the substrate thereby controlling the height of the air gap and therefore whether the pixel is bright or dark. In order to displace the membrane, relatively high voltages, on the order of tens of volts, must be applied to the addressable electrode.
It would be advantageous to have a flat panel display that uses ambient light, without the need for a separate light source, and that can provide high quality high contrast images while operating at low voltages with low power consumption.
An aspect of some preferred embodiments of the present invention is related to providing a micro-mechanical flat-panel display that uses ambient light and provides high-contrast images at substantially all viewing angles with respect to the plane of the display.
An aspect of some preferred embodiments of the present invention is related to providing a flat-panel display that operates with low power consumption.
An aspect of some preferred embodiments of the present invention is related to providing a flat-panel display that operates using electrical power supplied at low voltages.
An aspect of some preferred embodiments of the present invention relates to providing a flat-panel display that provides black and white and/or gray level images.
An aspect of some preferred embodiments of the present invention relates to providing a flat-panel display that provides color images.
An aspect of some preferred embodiments of the present invention relates to providing a micro-mechanical flat-panel display formed on a substrate and having pixels that comprise a moveable element.
In a preferred embodiment of the invention, the moveable element is formed in the shape of a thin planar panel having first and second relatively large face surfaces and thin edges. The panel, hereinafter referred to as a xe2x80x9cflipperxe2x80x9d, is hinged to the substrate in such a way that it is rotatable from one to the other of two limiting positions about an axis of rotation that is parallel to the surface of the substrate. The limiting positions are hereinafter referred to as xe2x80x9conxe2x80x9d and xe2x80x9coffxe2x80x9d positions. The flipper is preferably at least partly formed from a conducting material.
In the on position the first face surface faces a user looking at the display and is visible to the user. The second face surface of the flipper faces the substrate, facing away from the user, and is not visible to the user. In the off position the second face surface faces the user and is visible the user while the first face surface faces the substrate. Preferably, in the on and off positions, the plane of the flipper is close to and substantially parallel to the surface of the substrate. Preferably, the flipper rotates through approximately 180xc2x0 about the axis of rotation to rotate between on and off positions.
According to an aspect of some preferred embodiments of the present invention, rotation of the flipper is controllable so that the flipper is bistable. The flipper is either in the on position or in the off position and remains in one position until it is controlled to rotate to the other position. When the flipper is either in the on or off position the pixel consumes little or substantially no energy.
An aspect of some preferred embodiments of the present invention relates to providing addressable electrodes for each pixel in the substrate to which voltages are applied in different configurations so as to control rotation of the pixel""s flipper. For some voltage configurations applied to the electrodes, electrostatic forces generated between the flipper and the electrodes prevent the flipper from rotating between on and off positions. In these voltage configurations, substantially no current flows in the pixel and therefore the pixel consumes little or no energy. In other voltage configurations, electrostatic forces between the flipper and the electrodes generate a torque that rotates the flipper from one to the other of the on and off positions.
According to another aspect of some preferred embodiments of the present invention, the first face surface of the flipper in a pixel has a first color and the second face surface of the flipper has a second color. In addition, substantially all surfaces in the pixel that are visible when the flipper is in the on position, in which position the first face surface of the flipper is visible, are colored to have the same color as the first face surface of the flipper. Similarly, substantially all surfaces in the pixel that are visible when the flipper is in the off position, in which position the second face surface of the flipper is visible, are colored to have the same color as the second face surface of the flipper. As a result when the flipper is in the on position the pixel appears to have the first color and when the flipper is in the off position the pixel appears to have the second color.
In some preferred embodiments of the present invention the first color is white and the second color is black. In these preferred embodiments of the present invention pixels in the display are white when the flipper is in the on position and black when the flipper is in the off position and the display provides black and white images.
In some preferred embodiments of the present invention in which the first color is white and the second color is black, gray level images are provided. A gray level for a pixel is achieved, in accordance with a preferred embodiment of the present invention, by switching the pixel""s flipper between on and off positions so rapidly that the brain does not discern that the pixel is either black or white. Instead the brain perceives that the pixel is gray. The gray level perceived is determined by the ratio between the times that the flipper is in the on position and the off position.
In some preferred embodiments of the present invention gray level images are achieved by grouping pixels in a flat panel display into xe2x80x9csuper-pixelsxe2x80x9d. A super pixel comprises a plurality of pixels, for example three pixels, each of which is contiguous with at least one other pixel in the super pixel. A super pixel is small enough so that the eye does not distinguish whether a single pixel in the super pixel is black or white. Instead the eye integrates the stimuli received form the pixels in the super pixel and perceives an average of the received stimuli which is a gray level. For example, a super pixel with three black and white pixels can provide four gray levels of luminance.
In other preferred embodiments of the present invention the first color of pixels in a super pixel is red (R), green (G) or blue (B) and the second color is black. Pixels in the super pixel are therefore R, G or B when their flipper is in an on position and black when their flipper is in an off position. Super pixels comprising xe2x80x9ccolorxe2x80x9d pixels are useable, in accordance with a preferred embodiment of the present invention to provide a color flat-panel display.
An aspect of some preferred embodiments of the present invention relates to providing a pixel, hereinafter referred to as a xe2x80x9cmulti-flipper pixelxe2x80x9d that comprises at least two flippers. The axes about which flippers rotate between on and off positions are congruent or parallel and close to each other. The flippers are flipped back and forth between on and off positions and lie on each other in much the same way that pages in a book are flipped back and forth and lie on each other when the book is lying open on a table.
There is therefore provided in accordance with a preferred embodiment of the present invention a visual display comprising a plurality of pixels each of which comprises: a surface having an area less than 1 square millimeter comprising first and second regions having surface finishes; and a thin planar panel having first and second sides having surface finishes, wherein the panel is rotatably coupled to the surface so as to rotate between a first and a second position about an axis parallel to the surface; wherein the panel in the first position is positioned over the first region with its second side facing the first region and wherein in the second position the panel is positioned over the second region with its first side facing the second region.
Preferably when the panel is in the first position it obscures substantially all of the first region. Additionally or alternatively, when the panel is in the second position it preferably obscures substantially all of the second region.
In some preferred embodiments of the present invention the plurality of pixels is produced using micro-machining technology. The surface in some preferred embodiments of the present invention has an area less than 0.25 square millimeters. The surface in some preferred embodiments of the present invention has an area less than 5000 square microns. In some preferred embodiments of the present invention the surface has an area less than 2000 square microns.
According to some preferred embodiments of the present invention the first and second regions of the surface have first and second planar electrodes respectively. Preferably, at least one of the first and second electrodes has at least one non-conducting protuberance on its surface.
Additionally or alternatively, the panel is preferably formed from a conducting material. Preferably, at least one side of the panel has at least one non-conducting protuberance thereon. Additionally or alternatively, the first and second sides preferably have a non-conductive coating.
Alternatively or additionally, the panel is preferably rotated between first and second positions by electrostatic forces acting on the panel that are generated by applying voltages to the first and second electrodes and to the panel. Preferably, the panel is rotated from the first position to the second position by grounding the second electrode and applying a same voltage to the first electrode and the panel. Preferably, the panel is rotated from the second position to the first position by grounding the panel and the second electrode and applying a voltage to the first electrode. Alternatively or additionally, the panel is preferably rotated from the second position to the first position by applying a same voltage to the second electrode and the panel and grounding the first electrode.
In some preferred embodiments of the present invention, the panel is rapidly rotated between first and second positions in a time shorter than the response time of the eye so that the pixel appears to have a finish that is a mix between the finishes of the first side and the second region and the finishes of the second side and the first region.
In some preferred embodiments of the present invention the finish of the first region and the finish of the second side of the panel are the same. In some preferred embodiments of the present invention the finish of the second region and the finish of the first side of the panel are the same. In some preferred embodiments of the present invention the finish of the first region appears white. The finish of the first region displays a color that is a color of a tristimulus set of colors in some preferred embodiments of the present invention. The finish of the first region is luminescent in some preferred embodiments of the present invention. In some preferred embodiments of the present invention the finish of the second region displays a color of a tristimulus set of colors. The finish of the second region is luminescent in some preferred embodiments of the present invention. In some preferred embodiments of the present invention the finish of the second region appears black.
In some preferred embodiments of the present invention, at least one pixel of the plurality of pixels comprises at least one additional thin panel that has first and second sides having surface finishes and the at least one additional panel is rotatably coupled to the surface of the at least one pixel so as to rotate between first and second positions about an axis that is parallel to the surface.
Preferably, all the axes about which panels of the at least one pixel rotate are substantially coincident. Additionally or alternatively, panels of the at least one pixel that are in the first position are preferably positioned one over the other in a stack over the first region with their second sides facing the first region and panels in the second position are positioned one over the other in a stack over the second region with their first sides facing the second region. Preferably, a top-most panel in a stack of panels substantially obscures all panels below the top-most panel and the first region or the second region so that at any one time the at least one pixel displays only two of the surface finishes.
All panels of the at least one pixel are preferably formed from conducting material. Preferably, at least one side of at least one panel of the at least one pixel has at least one non-conducting protuberance thereon. Additionally or alternatively at least one side of at least one panel of the at least one pixel has a non-conducting coating.
Additionally or alternatively, panels of the at least one pixel are rotated between the first and second positions by electrostatic forces acting on the panels, the electrostatic forces being generated by applying voltages to the first and second electrodes and to panels of the at least one pixel.
Preferably, a topmost panel in a stack of panels in the first position is rotated to a second position with all panels in the first position and the first electrode grounded. Preferably when there is at least one panel in the second position, a voltage is applied to a topmost panel in the second position and the second electrode is grounded to rotate the topmost panel in the first position. When there are no panels in the second position preferably a voltage is applied to the second electrode to rotate the topmost panel in the first position.
Additionally or alternatively, a topmost panel in a stack of panels in the second position is rotated to a first position with all panels in the second position and the second electrode grounded. Preferably, when there is at least one panel in the first position, a voltage is applied to a topmost panel in the first position and the first electrode is grounded to rotate the topmost panel in the second position. Preferably, when there are no panels in the first position a voltage is applied to the first electrode to rotate the topmost panel in the second position.
Alternatively or additionally, a topmost panel of at least one panel in the second position is rotated to a first position by grounding the first electrode and applying a first voltage to the topmost panel in the second position. Preferably, when there is at least one panel in the first position a second voltage is applied to a topmost panel of the at least one panel in the first position and all other panels in the first position are grounded and wherein the second voltage is different from the first voltage. Additionally or alternatively, when there is at least one panel beneath the topmost panel in the second position, the first voltage is applied to a panel immediately below the topmost panel in the second position and all other panels in the second position and the second electrode are grounded. Alternatively or additionally, when there are no panels below the topmost panel in the second position the first voltage is applied to the second electrode.
In some preferred embodiments of the present invention, when at least one panel of the at least one pixel is in the first position and at least one panel is in the second position, the first side of a topmost panel in the first position and the second side of a topmost panel in the second position have a same finish. Preferably, the first region and the second side of a topmost panel in the second position have a same finish when all of panels of the at least one pixel are in the second position. Preferably, the second region and the first side of a topmost panel in the first position have a same finish when all panels of the at least one pixel are in the first position. Preferably, no two same finishes display a same color.
In some preferred embodiments of the present invention each of the same finishes displays a different gray level.
In some preferred embodiments of the present invention at least one of the same finishes is luminescent.
In some preferred embodiments of the present invention the at least one pixel comprises two panels. Preferably, each of the same finishes is a different color of a tristimulus set of colors.
In some preferred embodiments of the present invention a tristimulus set of colors is RGB.
In some preferred embodiments of the present invention, at least one panel of at least one pixel of the plurality of pixels is formed with at least one through hole near an edge thereof. Preferably, the at least one pixel comprises at least one bracket fastened to the surface, the at least one bracket having a U-shaped member having legs wherein, the U-shaped member passes through one of the at least one through hole so as to rotatably mount the at least one panel to the surface.
Preferably, the at least one panel is formed with at least one slot in the edge that joins with one of the at least one through hole through which a U-shaped member passes. Preferably the bracket of the U-shaped member that passes through a through hole joining with a slot comprises a septum that is positioned in the slot and wherein the septum limits motion of the at least one panel parallel to the edge.
In some preferred embodiments of the present invention at least one panel of at least one pixel of the plurality of pixels is formed with a protuberance at both ends of a single edge thereof. Preferably, the at least one pixel comprises two brackets fastened to the surface of the pixel, wherein each bracket comprises a U-shaped member having two legs wherein the U-shaped member of each bracket loops around a different one of the protuberances so as to rotatably mount the at least one panel to the surface. Preferably, at least one of the brackets has a surface that presses against an end of one of the protuberances wherein the surface limits motion of the at least one panel parallel to the single edge.
Additionally or alternatively the at least one panel is formed with clearance slots that enable the at least one panel to rotate from the first position to the second position without the at least one panel making physical contact with a bracket that couples a different one of the at least one panel to the surface.
Alternatively or additionally at least one of the brackets is preferably fastened to the surface of the at least one pixel at a single localized region of the bracket that is located near to one of the legs. Alternatively or additionally at least one of the brackets is preferably fastened to the surface of the at least one pixel at two localized regions of the bracket wherein each of the localized regions is located near to a different one of the legs.
Alternatively or additionally at least one of the brackets that couples the at least one panel to the surface of the at least one pixel is preferably formed from a conducting material. Preferably, the surface of the at least one pixel comprises at least one electrode in addition to the first and second electrodes. Preferably, the at least one bracket formed from the conducting material is fastened to one of the at least one additional electrodes. Preferably, when regions of the at least one panel are in physical contact with the electrode or the conducting bracket, the panel is in electrical contact with the electrode. Preferably, voltage is applied to the panel by applying voltage to the electrode.
In some preferred embodiments of the present invention, the first and second regions of the surface of at least one pixel of the plurality of pixels are planar and wherein an angle between the plane of the first region and the plane of the second region is less than 180xc2x0. Preferably, the angle is greater than 140xc2x0. More preferably the angle is greater than 160xc2x0.
There is further provided in accordance with a preferred embodiment of the present invention a micro-machined bracket for mounting a shaft to a surface so that the shaft is rotatable comprising: a U-shaped member having two legs connected by a bridging element; and a base member attached to one of the legs; wherein the base member is attached to the surface and the shaft is captured between the surface and the legs and bridging element of the U-shaped member.
There is further provided in accordance with a preferred embodiment of the present invention a micro-machined bracket for mounting an element comprising two collinear shafts to a surface so that the element is rotatable about the shafts and wherein the shafts are separated by a space, the bracket comprising: a U-shaped member having two legs connected by a bridging element; a base member attached to one of the legs; and a septum; wherein one of the base member is attached to the surface and the shaft is captured between the surface and the legs and bridging element of the U-shaped member and wherein the septum is located in the space between the shafts.